To complete a well, one or more formation zones adjacent a wellbore are perforated to allow fluid from the formation zones to flow into the well for production to the surface or to allow injection fluids to be applied into the formation zones. Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing to line the wellbore. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.
Perforating systems typically comprise one or more shaped charge perforating guns strung together. A perforating gun string may be lowered into the well and one or more guns fired to create openings in the casing and/or a cement liner and to extend perforations into the surrounding formation.
Shaped charge guns known in the art for perforating wellbores typically include a shaped charge liner. A high explosive is detonated to collapse the liner and ejects it from one end of the shaped charge at a very high velocity in a pattern called a “jet”. The jet penetrates and perforates the casing, the cement and a quantity of the earth formation. In order to provide perforations which have efficient hydraulic communication with the formation, it is known in the art to design shaped charges in various ways to provide a jet which can penetrate a large quantity of formation, the quantity usually referred to as the “penetration depth” of the perforation. The jet from the metal liners also may leave a residue in the resulting perforation, thereby reducing the efficiency and productivity of the well.
Furthermore, once a shape charge gun has been fired, in addition to addressing the issues regarding the residual liner material left in the perforation, the components other than the liner must generally also be removed from the wellbore, which generally require additional costly and time consuming removal operations.
Therefore, perforation systems and methods of using them that incorporate liners and other components formed from materials that may be selectively removed from the wellbore are very desirable.